JP2005255550A - Method for recovery of ester monomer from photographic film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for recovering valuable components, especially an ester monomer from a photographic film in high purity and efficiency. <P>SOLUTION: An ester monomer is recovered from a photographic film having a photographic image layer laminated on a polyester base film. The recovering method comprises (1) a step to peel the photographic image layer by immersing flakes of the photographic film in an aqueous solution of an alkali compound and heating at 50-100°C to dissolve or peel the photographic image layer, (2) a flake-separation step to separate the flakes from a liquid mixture obtained by the photographic image layer peeling step, (3) a depolymerization step to depolymerize the polyester component of the flake separated by the flake separation step with a diol in the presence of a depolymerization catalyst and (4) a monomer purifying and recovering step to purify the depolymerized solution. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for recovering ester monomers from photographic film. More specifically, the present invention relates to a method for efficiently recovering an ester monomer by separating a base film and a photographic image layer from a photographic film in which a photographic image layer is laminated on a polyester base film.

  A photographic film is usually subjected to an easy-contact treatment or an easy-contact layer on at least one side of a base film made of polyester, and then a photosensitive silver compound such as silver halide is finely dispersed in an aqueous gelatin solution. The photographic emulsion solution is coated and dried to form a photographic emulsion layer, and a protective layer made of gelatin is formed thereon.

  Photographic films are produced and used in large quantities for commercial use. For example, X-ray photographic films and plate-making films are used in large quantities in the medical and publishing / printing fields, respectively. These photographic films are usually discarded after use, but since these films contain a large amount of expensive silver, it has been practiced to collect the silver.

  Silver recovery is usually performed by a method (dry method) in which a used photographic film is once incinerated in an incinerator, and the generated ash is recovered and the silver component is recovered as metallic silver by refining or electrolysis. However, the dry method has a disadvantage that the polyester constituting the film cannot be reused at all. In addition, from the viewpoint of environmental pollution, there are problems that a large amount of combustion gas is generated, the combustion temperature of polyester is high, the furnace body is damaged, and the generation rate of oxidant is increased.

  As a silver recovery method, used photographic film is crushed and immersed in an aqueous solution containing sodium hydroxide or an enzyme that degrades gelatin, and the gelatin layer on the film surface is dissolved or decomposed to disperse silver particles in the solution. Thereafter, a method (wet method) in which silver fine particles are filtered and recovered as metallic silver by electrolysis or refining treatment has been used for some time. However, a large amount of waste liquid is generated in the wet method, but in general, the treatment of the waste liquid is far more technically and economically than the gas treatment. Also, with regard to the waste liquid of the wet method, there is a problem with the treatment method and cost for keeping the concentration of harmful substances after treatment within the environmental standard value.

  As a method of recovering the silver component from used photographic film, the photographic emulsion layer (photographic image layer) of the used photographic film is swollen with water or warm water, and the photographic emulsion layer is mechanically caused by friction (rotary drying washer). Has been proposed in which a photographic emulsion layer component (a component containing silver) is refined from the film. It has been shown that the film after the peeling treatment can be used as a plastic recycling raw material (Patent Document 1). However, there is no disclosure about a specific method using a film as a recycled raw material.

  In addition, the crushed used photographic film is dipped in warm water to weaken the adhesive strength of the photographic emulsion layer (photographic image layer), drained, and then dry-washed (with a rod-shaped pin placed vertically on the internal rotating disk) A so-called pin-type crusher is used to peel silver salt particles from a polyethylene terephthalate film and recover them (Patent Document 2).

When the base film from which the photographic emulsion layer (photographic image layer) has been peeled off by the method described in Patent Documents 1 and 2 is to be used as a plastic recycling raw material, in reality, a colorant (pigment, dye, etc.) is contained in the film. Is included and has a problem that it can be reused only for extremely few applications.
Japanese Patent Laid-Open No. 11-181533 JP 2000-237733 A

  An object of the present invention is to provide a method for recovering an ester monomer from a photographic film in which a photographic image layer is laminated on a polyester base film. Another object of the present invention is to provide a method for recovering an ester monomer from a photographic film by an environmentally friendly method with less generation of combustion gas or waste liquid.

  The present inventors have intensively studied to develop a method for efficiently recovering ester monomers from a photographic film in which a photographic image layer is laminated on a polyester base film. As a result, the photographic image layer is removed from the photographic film as efficiently as possible. For this purpose, the photographic film flakes are immersed in an aqueous solution of an alkali compound and heat-treated at a temperature of 50 to 100 ° C. When it is found that it is effective to dissolve or peel off the component), and the film obtained by this treatment is used, the colorant (pigment or dye) contained in the photographic film and the dust attached to the photographic film The present invention has been completed by finding a method capable of efficiently removing foreign substances such as and the like and efficiently recovering ester monomers by treatment such as depolymerization treatment and purification treatment.

That is, the present invention is a method for recovering an ester monomer from a photographic film in which a photographic image layer is laminated on a polyester base film,
(1) A photographic image layer peeling step in which flakes of a photographic film are immersed in an aqueous solution of an alkali compound and heat-treated at a temperature of 50 to 100 ° C. to dissolve or peel the photographic image layer;
(2) A flake separation step for separating flakes from the mixed liquid obtained in the photographic image layer peeling step,
(3) A depolymerization step in which the polyester component of the flakes separated in the flake separation step is depolymerized with a diol in the presence of a depolymerization catalyst, and (4) a depolymerization solution containing the ester monomer obtained in the depolymerization step is purified. A monomer purification and recovery step for obtaining a purified ester monomer by being treated;
The ester monomer is recovered from a photographic film containing

  In the present invention, the polyester component of the photographic film is preferably polyethylene terephthalate. In the photographic image layer peeling step, the amount of the alkaline compound aqueous solution used is preferably 1 to 10 parts by weight per 1 part by weight of photographic film flakes. The alkali compound is preferably an alkali metal compound or an alkaline earth metal compound compound. It is preferable that the content of the alkali compound in the aqueous solution of the alkali compound is 0.5 to 10% by weight. In the depolymerization step, the diol used is preferably ethylene glycol. It is preferable that the monomer purification / recovery step comprises filtration, adsorption, ion exchange, crystallization, low boiling point evaporation, molecular distillation, or a combination thereof. It is preferable that the monomer purification / recovery step includes a treatment for crystallization with a polar organic solvent other than glycol used in the depolymerization step.

  According to the present invention, a high purity ester monomer can be efficiently recovered from a photographic film. The present invention is extremely excellent in terms of environmental protection because it hardly generates combustion gas as in the conventional method and can recover the polyester component of the photographic film as a high purity ester monomer.

(Photo film)
The photographic film in the present invention is a film in which an easy-contact treatment or an easy-contact layer is formed on at least one side of a base film made of polyester, and then a photographic image (component) layer is laminated. is there. The photographic film may be either a wet type that requires a solution-type processing chemical (chemical) for development or a dry type that does not require the processing chemical. The photographic image layer may be subjected to exposure processing or may not be subjected to exposure processing.

Examples of wet type photographic image components include silver halide-gelatin emulsion, small amount of cellulose nitrate, cellulose ester, carbon, surfactant (dispersant, emulsifier), diazo substance, antistatic agent, electrostatic conductive substance, etc. Can be included. The coating amount (dry state) of the photographic image (component) layer is preferably 5 to 200 g / m ² . Further, the photographic image layer preferably has a protective layer made of gelatin or the like formed thereon.

There are various types of dry-type photographic image components depending on the development processing method (for example, laser exposure thermal development method, thermal head method, laser heat mode method, etc.), but photosensitive silver salt (for example, silver halide) Etc.), non-photosensitive silver salts (for example, organic acid silver), reducing agents (for example, resorcinols, m-aminophenols, m-phenylenediamines, 5-pyrazolones, phenols, p-alkoxyphenols) , Aminonaphthols, naphthalene-diols, etc.), crosslinkable compounds (eg, acrylic acid, methacrylic acid, styrene, vinyl ethers, vinyl esters, and derivatives thereof), toning agents (eg, phthalic acid derivatives, phthalazines) Etc.), spectral sensitizing dyes, carbon, laser sensitive components, etc. Nda (e.g., gelatin, hydroxyethyl cellulose, methyl cellulose, carbomethoxy cellulose, nylon, polyvinyl butyral, polyvinyl alcohol, polyvinyl benzal, polyvinyl pyrrolidone, polyvinyl methyl imidazole, polyhydroxyethyl acrylate, etc.) may be mentioned those containing. The coating amount of the photographic image component is preferably 5~300g / m ^2. Further, the photographic image component preferably has a protective layer made of gelatin or the like formed thereon.

  Photographic films in which layers of such photographic image components are laminated are produced and used in large quantities for commercial use. For example, X-ray photographic films and plate-making films are used in large quantities in the medical and publishing / printing fields, respectively.

  The easy-contact layer has an affinity between the polyester base film and the photographic image layer, and has a function of improving the adhesion (adhesion) between the two. Such an easy-contact layer is preferably a water-soluble or water-dispersible resin having affinity for polyester.

  The water-soluble or water-dispersible resin is selected from water-soluble or water-dispersible polyester resins, polyester urethane resins, acrylic resins, ethylene ionomer resins, polyvinyl alcohol resins, and ethylene-vinyl alcohol resins. It is preferable that there is at least one. These resins preferably have a hydrophilic functional group in the molecular structure, and among them, a hydroxyl group, an ether group, an amide group, a carboxyl group, a phosphate ester group, a sulfonic acid group, an amino group, an imino group, and a carboxylic acid. Those containing at least one selected from a base, a sulfonate group and an ammonium base are preferred, and those containing at least one selected from a hydroxyl group, a carboxyl group, a sulfonate group and a carboxylate group are particularly preferred.

  Specific examples of water-soluble or water-dispersible resins include candy starch, potato starch, wheat starch, corn starch, konnyaku, funari, agar, sodium alginate, trooaoi, tragacanth gum, gum arabic, dextran, levan, glue, gelatin, casein Collagen, viscose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, soluble starch, carboxymethyl starch, dialdehyde starch, polyvinyl alcohol, sodium polyacrylate, polyethylene oxide, polyacrylamide, poly Preferable examples include water-soluble resins such as acrylic acid and poly N-vinylpyrrolidone. These may be used alone or in combination of two or more.

  The photographic film in the present invention is usually such a photographic film, and is subjected to processing such as photographing, development and fixing to form a desired photographic image, for example, an X-ray photographic image, a plate-making image, etc. on the base film. Is. This photographic film may be used for any purpose. Most of them are usually monochrome photographic films, but particularly large amounts are X-ray photographic films in the medical field and monochrome films for plate making in the publishing / printing field, and these are particularly useful as raw materials for the present invention. Useful.

  The polyester constituting the base film of the photographic film is preferably a linear aromatic polyester, and further an aromatic polyester having an aromatic dicarboxylic acid as the main acid component and a C2-8 glycol as the main glycol component. Polyethylene terephthalate is particularly preferable. Such a polyester is preferably a homopolymer, but may be a copolymer obtained by copolymerizing the third component in a small proportion (for example, preferably 20 mol% or less, more preferably 15 mol% or less with respect to the total acid component). good. For example, copolymer components of copolyethylene terephthalate include dicarboxylic acid components such as phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and adipic acid, and glycol components such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, and cyclohexanedimethanol. Can be mentioned. Further, the polyester may be a blend polymer obtained by mixing other condensed resin in a small proportion (for example, preferably 20% by weight or less based on the total weight).

  These polymers usually contain modifiers (for example, lubricants, colorants, stabilizers, etc.) for imparting properties required for a base film. This film may be a single layer film or a laminated film in which two or more layers are laminated. In the case of a laminated film, two or more kinds of films made of the above-described polymer may be bonded together. In some cases, components that are considered to be harmful to the environment, such as vinyl chloride, may adhere to this film, but even in this case, vinyl chloride is removed at the stage of film depolymerization and purification. Can do. Even if a small amount of vinyl chloride is used, dioxins are generated during incineration, and this is a particular problem for environmental protection. Therefore, the method of the present invention for recovering silver or a polyester component occupying a large proportion without incineration of the film is preferable in this respect.

  The photographic film in the present invention has the purpose of absorbing light in a specific wavelength range, that is, the purpose of halation and irradiation, the purpose of controlling the spectral composition of light to be incident on the photographic image layer by providing a filter layer, or visual recognition. For the purpose of improving properties, a film in which a base film is colored with a dye, a pigment or the like, or a filter layer colored with a dye is provided as an undercoat layer is also included. Examples of such dyes include oxonol dyes having a pyrazolone nucleus and a barbituric acid nucleus, azo dyes, azomethine dyes, anthraquinone dyes, arylidene dyes, styryl dyes, triarylmethane dyes, merocyanine dyes, and cyanine dyes. it can.

<Photographic image layer peeling process>
In the photographic image layer peeling step in the present invention, flakes obtained by subjecting a photographic film to treatment such as pulverization, cutting, and breakage are immersed in an aqueous solution of an alkali compound and heat-treated at a temperature of 50 to 100 ° C. to produce a photographic image. This is a step of dissolving or peeling the layer.

  Processing methods such as pulverization, cutting, and breakage using photographic film as flakes are not particularly limited, but it is preferable to perform processing using, for example, a hammer mill, a high-speed rotation mill, a roller mill, or the like. The shape of the flakes is not particularly limited, but may be an irregular shape such as a triangle, a square, or a rectangle. The thickness is usually 75 to 350 μm. The size is preferably about 1 to 10 cm square, more preferably 2 to 8 cm square, and particularly preferably about 3 to 6 cm square, although it depends on the conditions of the step of peeling the photographic image component and the depolymerization conditions.

  Examples of alkali compounds include alkali metal or alkaline earth metal hydroxides, carbonates, oxalates, acetates, alkoxides, and the like. Examples of the alkali metal include lithium, sodium, and potassium. Moreover, magnesium, calcium, etc. can be illustrated as an alkaline-earth metal. Of these alkali (earth) metals, sodium metal is most preferred.

  More specifically, examples of the alkali compound include potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium methylate and the like. These may be used alone or in combination of two or more. The content of the alkali compound in the aqueous solution of the alkali compound is preferably 0.5 to 10% by weight, more preferably 4 to 8% by weight.

  The photographic image layer peeling step is a step of dissolving or peeling the photographic image layer in the presence of alkali metal ions or alkaline earth metal ions of these alkali compounds.

  The amount of the alkaline compound aqueous solution used is preferably 1 to 10 parts by weight, more preferably 2 to 5 parts by weight, per 1 part by weight of the photographic film flakes. If the amount used is too small, sufficient peeling cannot be expected. On the other hand, if the amount used is too large, the peeling effect is hardly changed and it is not economical.

  Although the temperature of heat processing is 50-100 degreeC, Preferably it is 60-95 degreeC, More preferably, it is 70-90 degreeC. When the heat treatment temperature is less than 50 ° C., peeling of the photographic image components does not proceed. On the other hand, when the heat treatment temperature exceeds 100 ° C., the alkaline compound aqueous solution evaporates more than necessary.

  The time for the heat treatment is the time for the photographic image layer to be dissolved or peeled off in the aqueous solution of the alkali compound depending on the temperature of the heat treatment, preferably 1 to 120 minutes, more preferably 3 to 100 minutes, particularly preferably 5 to 60. Minutes.

  In this photographic image layer peeling step, the photographic image layer provided on at least one side of the photographic film is dissolved in an aqueous solution of an alkali compound or peeled from the base film.

<Flake separation process>
In the flake separation step in the present invention, the solid and the solution are separated from the mixed solution obtained in the photographic image layer peeling step, the solid is washed with water to remove the alkali, and then the polyester flakes are separated from the solid. This is a step of separating into a peeled photographic image layer.

  As a means for separating the solid from the mixed solution, any separation means can be used, but filtration is simple and preferable. The separated solid is subjected to a water washing treatment to remove alkali. The solution separated from the solid (an aqueous solution of an alkali compound) can be reused after removing the fine particles by filtration or the like (for example, passing the solution through a strainer), correcting the alkali.

  The solid material from which the alkali has been removed by the water washing treatment is a mixture of polyester flakes and the peeled photographic image layer. As a means for separating the polyester flakes from the mixture, it is preferable to disperse the mixture in water and separate it by operations such as specific gravity separation and decantation. The separated polyester flakes are dehydrated and dried for use in the next step (for example, depolymerization step). The moisture content of the polyester flakes is preferably as small as possible, and is preferably dried to 0.1 to 0.6% by weight, for example. On the other hand, when the photographic image layer separated from the polyester flakes contains a valuable material such as silver, it can be dried to collect the valuable material.

<Depolymerization process>
The depolymerization step in the present invention is a step of depolymerizing the polyester component of the flakes (polyester flakes) separated in the flake separation step with a diol in the presence of a depolymerization catalyst. Examples of the diol include aliphatic glycols having 2 to 8 carbon atoms, polyester ester monomers, oligomers thereof, and the like. These may be used alone or in combination of two or more, but it is particularly preferable to use a combination of an aliphatic glycol having 2 to 8 carbon atoms and a polyester ester monomer and / or an oligomer thereof. For example, the polyester component of the base film separated in the flake separation step is pre-depolymerized using the ester monomer and / or oligomer thereof, and the pre-depolymerized product is depolymerized with an aliphatic glycol to obtain a depolymerization solution. Is preferable.

  Hereinafter, description will be made using polyethylene terephthalate as a representative of polyester, bis (2-hydroxyethyl) terephthalate and / or its oligomer, and ethylene glycol as a representative of diol.

  For example, polyethylene terephthalate is first depolymerized mainly from its ester monomer, bis (2-hydroxyethyl) terephthalate and / or its oligomer (preferably an oligomer having a degree of polymerization in the range of about 2 to 10). Predepolymerization (predepolymerization) by contacting with an agent (preferably, distillation residue of crude BHET) at an elevated temperature, and then further depolymerization (main depolymerization) using excess ethylene glycol It is preferable to prepare a decomposition product solution (depolymerization solution) containing bis (2-hydroxyethyl) terephthalate as a main solid content. This ethylene glycol may be purified, but for example, crude ethylene glycol containing a small proportion of other diols, crude ethylene glycol generated in crystallization / solid-liquid separation, or crude ethylene glycol and purified ethylene glycol A mixture may be used.

  In the pre-depolymerization, the amount ratio of polyethylene terephthalate and diol bis (2-hydroxyethyl) terephthalate and / or its oligomer is bis (2-hydroxyethyl) terephthalate and / or its oligomer per part by weight of polyethylene terephthalate. 0.1 to 4.5 parts by weight, more preferably 0.1 to 2.0 parts by weight, and particularly preferably 0.1 to 1.0 parts by weight. The temperature for the preliminary depolymerization is preferably 180 to 290 ° C, more preferably 190 to 270 ° C, and particularly preferably 200 to 260 ° C. The reaction time is preferably 0.1 to 5.0 hours, more preferably 0.3 to 1.5 hours. The decomposition product obtained by preliminary depolymerization preferably has a degree of polymerization of about 2 to 40, more preferably 3 to 30.

  The depolymerization reaction (predepolymerization reaction) between the decomposition product (preliminary depolymerization product) and ethylene glycol is preferably 170 to 265 ° C, more preferably 180 to 230 ° C. The amount ratio of this pre-depolymerized product to ethylene glycol is preferably 0.5 to 8.0 parts by weight, more preferably 2.0 to 7.0 parts by weight, per 1 part by weight of the pre-depolymerized product. . If the amount of the pre-depolymerized product is too small relative to ethylene glycol, the amount of bis (2-hydroxyethyl) terephthalate produced will be less than the saturated solubility in ethylene glycol, resulting in a total liquid volume subjected to ion exchange treatment. On the other hand, bis (2-hydroxyethyl) terephthalate can only be obtained in an amount less than the maximum yield obtained, which is not economical. On the other hand, if the amount of the pre-depolymerized product is too large with respect to ethylene glycol, the oligomer of bis (2-hydroxyethyl) terephthalate increases and the yield of bis (2-hydroxyethyl) terephthalate decreases. On the other hand, if bis (2-hydroxyethyl) terephthalate is present in excess of the saturated solubility of ethylene glycol, bis (2-hydroxyethyl) terephthalate is deposited, so that the ion exchange treatment cannot be performed.

  It is preferable to use a depolymerization catalyst during the depolymerization treatment. Examples of the catalyst include sodium hydroxide, sodium carbonate, sodium methylate, zinc acetate and the like. Moreover, as the usage-amount, it is 0.05-0.50 weight% with respect to polyester, Furthermore, it is preferable that it is 0.15-0.40 weight%. The depolymerization reaction time is preferably 0.5 to 5.0 hours, more preferably 0.5 to 4.0 hours. The depolymerized product obtained by this reaction contains bis (2-hydroxyethyl) terephthalate as a main component, and a polymerization degree of 2 to 20 in a small proportion (for example, 20% by weight or less, further 10% by weight or less per total solute), Furthermore, 2-10 oligomers can be included.

  Moreover, when using ethylene glycol as a depolymerizing agent (diol) from the beginning, the depolymerization temperature is preferably 170 to 230 ° C, more preferably 190 to 220 ° C. The amount ratio of polyethylene terephthalate and ethylene glycol during depolymerization is preferably 1: 9 to 3: 7 by weight. If the amount of polyethylene terephthalate is too small relative to ethylene glycol, the amount of BHET produced will be less than the saturated solubility of ethylene glycol and less than the maximum yield obtained for the total liquid volume subjected to ion exchange treatment. However, since bis (2-hydroxyethyl) terephthalate cannot be obtained, it is not economical. On the other hand, when the amount of polyethylene terephthalate is too large relative to ethylene glycol, the oligomer of bis (2-hydroxyethyl) terephthalate increases and the yield of bis (2-hydroxyethyl) terephthalate decreases. On the other hand, if bis (2-hydroxyethyl) terephthalate is present in excess of the saturation solubility of ethylene glycol, bis (2-hydroxyethyl) terephthalate is deposited, so that the ion exchange treatment cannot be performed.

  It is preferable to use a depolymerization catalyst during the depolymerization treatment. Examples of the catalyst include sodium hydroxide, sodium carbonate, sodium methylate, zinc acetate and the like. Moreover, as the usage-amount, it is 0.05-0.50 weight% with respect to polyester, Furthermore, it is preferable that it is 0.15-0.40 weight%. The depolymerization reaction time is preferably 0.5 to 7.0 hours, more preferably 0.5 to 5.0 hours.

  The depolymerization is preferably carried out while providing a rectifying column in the depolymerization reaction apparatus and distilling water from the reaction solution out of the system. At that time, the evaporated ethylene glycol is preferably returned to the system. By performing the depolymerization reaction in this manner, the amount of water in the decomposition product solution (depolymerization solution) can be reduced, so that the hydrolysis reaction of bis (2-hydroxyethyl) terephthalate can be suppressed. It is preferable to adjust so that the amount of water contained in the solution is 0.5% by weight or less. The amount of moisture can be obtained by measuring the solution with a Kyoto Electronics Industry Co., Ltd. MK-SS type Karl Fischer moisture meter.

  The depolymerization solution usually has bis (2-hydroxyethyl) terephthalate as the main solute, ethylene glycol as the main solvent, and is contained in the raw material polyester (especially polyethylene terephthalate) as a secondary solute, or during the depolymerization reaction. Including diethylene glycol ester (DEG ester) generated by side reaction, bis (2-hydroxyethyl) terephthalate oligomer and mono (2-hydroxyethyl) terephthalate as other solute components, and raw material as non-solute component The diethylene glycol component contained in the polyester, the free diethylene glycol by the diethylene glycol component generated by the side reaction during the depolymerization reaction, and the like can be included. Furthermore, catalysts used for depolymerization (for example, alkali compounds), catalysts used for polyester polycondensation reactions (for example, antimony compounds, germanium compounds, etc.), stabilizers such as phosphorus compounds, and various unpredictable stains, etc. Impurity ions derived from can be included.

  The solid content of the depolymerization solution is mainly composed of bis (2-hydroxyethyl) terephthalate, and the proportion of the oligomer is reduced to 1 to 30% by weight, further 2 to 25% by weight, especially 3 to 20% by weight. . The concentration of the solid content is preferably 10 to 30% by weight, more preferably 15 to 25% by weight.

<Monomer purification and recovery process>
The monomer purification / recovery step of the present invention preferably comprises filtration treatment, activated carbon treatment, ion exchange treatment, crystallization treatment, low boiling point evaporation treatment, molecular distillation treatment, and combinations thereof.

(Filtering process)
The filtration treatment in the monomer purification and recovery step in the present invention is a step of separating and removing solid foreign substances from the depolymerization solution containing the ester monomer obtained in the depolymerization step. Examples of the solid foreign matter include those composed of components of a photographic image layer and an undercoat layer that have not been dissolved or peeled off in the photographic image layer peeling step, fine particles such as pigments contained in the base film, and depolymerizing agents (diols). The glycol insoluble component contained etc. can be mentioned. Examples of the filtration treatment include suction filtration treatment, pressure filtration treatment, solid-liquid separation treatment, and specific gravity separation treatment. When separating and removing the suspended solids, it is preferable to use a method of first removing relatively large solid foreign matters (first-stage filtration treatment) and then removing fine particles such as pigment (second-stage filtration treatment).

  The first-stage filtration treatment is a treatment for removing the relatively large solid foreign matter by filtering the depolymerization solution. In this filtration treatment, the depolymerization solution is filtered at 160 to 260 ° C., preferably 180 to 220 ° C., and solid foreign matters that have not been decomposed by the depolymerization reaction, such as photographic images that have not been dissolved or removed in the photographic image layer peeling step It is preferable to remove a layer or an undercoat layer component. For example, it is preferable to pass the depolymerization solution through a metal strainer having a pore diameter of 0.1 to 2.0 mm.

  The second stage filtration process is a process for removing solid foreign matters that could not be removed by the first stage filtration process. In this filtration treatment, the depolymerization solution is cooled to 50 to 100 ° C., preferably 70 to 90 ° C., and solid foreign matters that cannot be removed by the first-stage filtration treatment, for example, solid foreign matters having an average particle diameter of about 1 to 500 μm. It is preferable that it is the process which filters. For example, it is preferable to filter the depolymerization solution by passing it through a filtration device filled with a filter medium made of 3 to 20 dtex fibers (polyester fiber, polypropylene fiber, etc.) with a porosity of 70 to 98%.

(Activated carbon treatment)
Among the monomer purification and recovery steps in the present invention, the activated carbon treatment is carried out by maintaining the depolymerization solution at a temperature of 50 to 100 ° C., preferably 70 to 90 ° C., and a space velocity of 0.1 to 5 in an adsorption tower packed with activated carbon. A treatment (activated carbon treatment) for passing liquid at 0 hr ⁻¹ is preferred. This adsorption treatment also removes a non-polar substance, for example, a colorant such as a pigment, and can be said to be a decolorization treatment. Examples of the activated carbon include “Dia Hope 006” and “Dia Hope 008” manufactured by Mitsubishi Chemical Corporation.

  Since the depolymerization solution after the activated carbon treatment contains activated carbon fine powder having an average particle diameter of about 1 to 500 μm, it is preferable to remove the activated carbon fine powder by filtration treatment. The filtration method can be removed by the same method as the second-stage filtration described above.

(Ion exchange treatment)
Among the monomer purification and recovery steps in the present invention, as an ion exchange treatment, the depolymerization solution is maintained at a temperature of 50 to 100 ° C., preferably 70 to 90 ° C., and a space velocity is applied to a decation tower packed with a cation exchanger. Cation exchange treatment is performed by passing the solution at ¹ to 12 hr ⁻¹ , preferably 4 to 9 hr ⁻¹ , and then passed through the connecting pipe for 3 seconds to 10 minutes, preferably 3 seconds to 5 minutes. The anion exchange treatment is preferably performed by passing the liquid through the packed deanion column at a space velocity of 0.5 to 10 hr ⁻¹ , preferably ¹ to 8 hr ⁻¹ . Preferable examples of the cation exchanger include cation exchange resin “Amberlite IR-120B” manufactured by Rohm and Haas. Moreover, as an anion exchanger, the mixture etc. of anion exchange resin "Amberlite IRA96SB" by Rohm and Haas company and a cation exchange resin "Amberlite IR-120B" etc. can be mentioned preferably, for example. The mixing ratio (volume ratio) of the anion exchange resin and cation exchange resin is preferably 1: 3 to 5: 1. By the ion exchange treatment, it is possible to remove metal ions such as a catalyst used in the production of polyester and ionic substances such as ionic dyes.

(Crystal treatment)
In the crystallization treatment, the crystallization treatment (I) for precipitating a solid content mainly composed of a polyester monomer from the depolymerization solution obtained by the ion exchange treatment, and the precipitate deposited in the crystallization treatment (I) and the solution are separated. The solid-liquid separation treatment (I) to obtain a solid (cake) and the crystallization treatment (II) in which the cake obtained in the solid-liquid separation treatment (I) is dissolved in a polar organic solvent other than glycol and recrystallized. It is preferable to comprise solid-liquid separation treatment (II) in which the precipitate precipitated in the crystallization treatment (II) and the solution are separated to obtain a solid content (cake).

  In the crystallization treatment (I), the solution after the ion exchange treatment (ion exchange treatment solution) is cooled in the crystallization tank from a temperature equal to or higher than the saturation solubility to a temperature in the range of 15 to 30 ° C. Maintaining the temperature for 1 to 12 hours, the ester monomer is precipitated so that the average particle size of the precipitate becomes 40 to 200 μm (measured by diluting 10 times with EG using SALD-200VER made by Shimadzu Corporation). Is preferred. When this ion exchange treatment solution is cooled from a temperature equal to or higher than the saturation solubility, it is preferably slowly cooled, for example, at a rate of 0.1 to 0.5 ° C./min.

The solid-liquid separation process (I) is a process for separating the solid (cake) from the solution containing the precipitate obtained by the crystallization process (I). Solid-liquid separation is preferably performed while maintaining the temperature of the crystallization treatment (I), that is, a temperature in the range of 15 to 30 ° C. The method is preferably performed by a method such as suction filtration, centrifugal separation, or pressure filtration. For example, in the case of pressure filtration, the precipitate is preferably filtered at a pressure of 1 to 2 MPa by a filter press using a filter cloth having an air permeability of ^{3 to 30} cm ³ / min · cm ² . It is preferable to filter using a filter paper having a retained particle diameter of 1 to 30 μm. The solid concentration in the cake separated by filtration is preferably 40 to 85% by weight. Organic coloring substances, diol-soluble impurities, by-products and the like that cannot be removed by activated carbon treatment or ion exchange treatment can be removed by crystallization / solid-liquid separation treatment.

  In the crystallization treatment (II), the cake obtained by the solid-liquid separation treatment (I) is dissolved in a polar organic solvent other than glycol at a temperature equal to or higher than the saturation solubility, and a temperature in the range of −10 to 30 ° C. from this temperature. The precipitate is maintained at a temperature in this range for 1 to 12 hours, and the average particle size of the precipitate becomes 40 to 200 μm (measured by diluting 10 times with EG using a Shimadzu SALD-200VER). Thus, it is preferable to treat the ester monomer. When the solution in which the cake is dissolved is cooled from a temperature equal to or higher than the saturation solubility, for example, it is preferably cooled at a rate of 0.1 to 1.5 ° C./min. Preferable examples of the polar organic solvent include aliphatic monoalcohols having 1 to 5 carbon atoms such as lower alcohols (for example, 2-propanol, 1-butanol and the like). By performing crystallization treatment with these organic solvents, impurities that could not be removed by a combination of activated carbon treatment, ion exchange treatment and crystallization treatment (I) can be removed.

  The cake obtained by the solid-liquid separation treatment (I) contains 15 to 60% by weight of a diol such as ethylene glycol used in the depolymerization step. This is because the diol has a high viscosity and is difficult to separate from the cake. Therefore, when the photographic base film contains a dye that is soluble in the diol used in the depolymerization step, a dye that cannot be completely removed may remain in the cake. In this case, the dye can be easily removed by performing a crystallization treatment using a polar organic solvent that can be easily separated from a cake such as a lower alcohol.

  Examples of such diol-soluble dyes include oxonol dyes having a pyrazolone nucleus and a barbituric acid nucleus, azo dyes, azomethine dyes, anthraquinone dyes, arylidene dyes, styryl dyes, triarylmethane dyes, merocyanine dyes, and cyanine dyes. .

Accordingly, the present invention is a method for recovering an ester monomer from a photographic film in which a photographic image layer is laminated on a polyester base film containing a diol-soluble dye,
(1) A photographic image layer peeling step in which flakes of a photographic film are immersed in an aqueous solution of an alkali compound and heat-treated at a temperature of 50 to 100 ° C. to dissolve or peel the photographic image layer;
(2) A flake separation step for separating flakes from the mixed liquid obtained in the photographic image layer peeling step,
(3) a depolymerization step of depolymerizing the polyester component of the flakes separated in the flake separation step with a diol in the presence of a depolymerization catalyst; and (4) a depolymerization solution containing an ester monomer obtained in the depolymerization step. Monomer purification and recovery step including treatment for crystallization with a polar organic solvent other than
A method of recovering ester monomers from a photographic film comprising:

The solid-liquid separation treatment (II) is a treatment for separating the cake from the solution containing the precipitate obtained by the crystallization treatment (II). The solid-liquid separation is preferably performed while maintaining the temperature of the crystallization treatment (II), that is, in the range of −10 to 30 ° C. The method is preferably performed by a method such as suction filtration, centrifugal separation, or pressure filtration. For example, in the case of pressure filtration, the precipitate is preferably filtered at a pressure of 1 to 2 MPa by a filter press using a filter cloth having an air permeability of ^{3 to 30} cm ³ / min · cm ² . It is preferable to filter using a filter paper having a retained particle diameter of 1 to 30 μm. The solid concentration in the cake separated by filtration is preferably 80 to 98% by weight.

(Low boiling point evaporation process)
The low boiling point evaporation treatment is performed by melting the cake obtained in the solid-liquid separation treatment (II) at 100 to 140 ° C. while distilling off the organic solvent to obtain a solid content mainly composed of an ester monomer. It is preferable to make it a melt with a content of 98 to 99.5% by weight. Next, the melt is introduced into an evaporator, the low boiling point component is evaporated under the conditions of a temperature of 130 to 170 ° C. and a pressure of 50 to 250 Pa, and the solid content containing the ester monomer as a main component is 99.5% by weight or more. It is preferable that By this treatment, residual low-boiling substances that cannot be removed by the crystallization / solid-liquid separation treatment can be removed.

(Molecular distillation treatment)
The molecular distillation treatment is preferably performed by introducing the melt subjected to the evaporation treatment into a falling film type molecular distillation apparatus and performing distillation (molecular distillation) under conditions of a temperature of 180 to 220 ° C. and a pressure of 25 Pa or less. By this treatment, high-boiling impurities such as oligomers can be removed, and an ester monomer having a purity of 98% by weight or more can be preferably obtained.

  By purifying the depolymerization solution by the above-described operation, it is possible to efficiently obtain a high-quality ester monomer, particularly preferably bis (2-hydroxyethyl) terephthalate (BHET). This purified bis (2-hydroxyethyl) terephthalate can be polymerized in the presence of a polymerization catalyst to produce high-quality (for example, excellent color tone) polyethylene terephthalate.

  As described above, the polyester film contains additives used in the production of polyester, for example, a catalyst, a colorant, a stabilizer, and the like, but may contain a trace amount of gelatin in some cases. Even in this case, according to the monomer purification / recovery step, high-purity ester monomer can be recovered. The optical density of the high-purity ester monomer is preferably 0.000 to 0.010, more preferably 0.000 to 0.006, and the purity is preferably 95% by weight or more, and more preferably 98% by weight or more.

  Therefore, in the present invention, it is obtained by filtration treatment for filtering the depolymerization solution containing the ester monomer obtained in the depolymerization step, activated carbon treatment for decolorizing the depolymerization solution obtained by filtration treatment with activated carbon, and activated carbon treatment. In the crystallization treatment (I), the crystallization treatment (I) for precipitating a solid content mainly composed of a polyester monomer from the depolymerization solution obtained by the ion exchange treatment, removing the ionic substance from the depolymerization solution. Solid-liquid separation treatment (I) for separating the deposited precipitate and solution to obtain a solid (cake), the cake obtained by solid-liquid separation treatment (I) is dissolved in a polar organic solvent other than diol and again Solid-liquid separation treatment (II), solid-liquid separation treatment to obtain a solid content (cake) by separating the precipitate from the crystallization treatment (II) and recrystallization treatment (II) and the solution. The cake obtained in II) is subjected to evaporation treatment. The ester monomer is recovered by a monomer purification and recovery process consisting of a low-boiling point evaporation process for removing low-boiling substances and a molecular distillation process for subjecting the crude ester monomer melt obtained by the low-boiling point evaporation process to a molecular distillation process. It is preferable to collect.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, the following Example does not limit this invention. The characteristics in the examples are measured by the following methods.
(1) Optical density 5 g of a sample was dissolved in methanol to give a 10 wt% methanol solution, and the cell length was 10 mm by UVmini-1240 (manufactured by Shimadzu Corporation), the blank was zero-point corrected using methanol, and this solution The absorbance at 380 nm was measured.
(2) Purity of ester monomer A sample of 50 mg is precisely weighed, a solution of about 100 ppm is prepared using chloroform, and this is analyzed by a liquid chromatographic method to obtain an ester monomer (for example, bis (2-hydroxyethyl) terephthalate). ).

[Example 1]
<Photographic image peeling process>
An X-ray photographic film (dry type, SD-P (manufactured by Konica Medical and Graphic Co., Ltd.)) whose base film is polyethylene terephthalate was cut into flakes of about 1 cm square. 75 g of an aqueous sodium solution was placed in a 300 ml glass separable flask equipped with a stirrer and heated to 85 ° C., and further stirred and heated under normal pressure for 40 minutes. As a result, the functional layer of the photographic film was peeled off from the blue base film. Was confirmed visually.

<Flake separation process>
The obtained solid-liquid mixture was cooled to room temperature and NO. The solid content was separated from the Buchner funnel covered with 1 filter paper through a suction bottle and filtered with a suction pump, and the alkali component (sodium hydroxide) of the solid content was washed away with water.

  The solid content was transferred to a 200 ml beaker, 100 g of water was added and stirred, and the decantation was repeated three times to separate the floating functional layer from the base film. This base film was subjected to a dehydration drying process to obtain 18 g of base film flakes mainly composed of polyethylene terephthalate.

<Depolymerization process>
7.6 g of this flake was charged with 42.4 g of ethylene glycol and 0.02 g of sodium hydroxide as a depolymerization catalyst, and charged into a 200-ml glass separable flask equipped with a stirrer and a rectifying tower. Depolymerization was performed by heating under reflux for an hour.

<Monomer purification and recovery process>
(Filtering process)
The resulting depolymerization solution (decomposition product solution) was colored blue. This depolymerized solution was passed through a basket strainer having a pore diameter of 1 mm to remove relatively coarse solid foreign matters that were not decomposed (depolymerized).

(Activated carbon treatment)
Next, the solution was cooled to 85 ° C., passed through a column packed with 6 dtex polypropylene fiber at a porosity of 85%, and then maintained at 85 ° C. with 50 ml of activated carbon (manufactured by Mitsubishi Chemical Corporation, Diahop 006). Was passed through the decolorization column packed with a space velocity (SV) of 3 hr ⁻¹ to adsorb and remove coloring substances and minute foreign matters.

(Ion exchange treatment)
Thereafter, the mixture was passed through a cation exchange column packed with 20 ml of a cation exchange resin (Rum & Haas, Amberlite IR-120B) at a space velocity (SV) of 7 hr ⁻¹ , and further 13.4 ml of an anion exchange resin (Rohm). The mixture was passed through an anion exchange column packed with a mixture of Andhers Amberlite IRA96SB) and 6.6 ml of a cation exchange resin (Rohm and Haas Amberlite IR-120B) at a space velocity (SV) of 7 hr ⁻¹ . To remove ionic substances in the solution.

(Crystal treatment)
This solution was cooled at a rate of 0.3 ° C./min from 85 ° C. to 25 ° C. with stirring, and kept at 25 ° C. for 60 minutes to precipitate crystals mainly composed of bis (2-hydroxyethyl) terephthalate. The solution in which the crystals are precipitated is referred to as NO. A Buchner funnel covered with 5A filter paper was passed through a suction bottle and filtered with a suction pump to separate the solid and liquid to obtain 15.3 g of a cake having a solid content concentration of 55% by weight. This cake was colored blue.

  This cake was transferred to a 200 ml beaker, mixed with 2-propanol so that the solid-liquid ratio was 1: 3 (weight ratio), and heated to 70 ° C. to completely dissolve the cake. This solution was cooled at a rate of 0.5 ° C./min from 70 ° C. to 0 ° C. with stirring, and kept at 0 ° C. for 60 minutes to precipitate crystals mainly composed of bis (2-hydroxyethyl) terephthalate. The solution in which the crystals are precipitated is referred to as NO. A Buchner funnel covered with 5A filter paper was passed through a suction bottle and filtered with a suction pump to separate the solid and liquid to obtain 8.2 g of a white cake having a solid content of 97% by weight.

(Low boiling point evaporation process)
This cake was heated to 120 ° C. in a nitrogen atmosphere and melted while distilling off the remaining 2-propanol, and the resulting melt was introduced into an evaporator, and remained under conditions of 133 Pa and 150 ° C. The low-boiling substances were evaporated to obtain a melt having a solid content concentration of 99.6% by weight.

(Molecular distillation treatment)
This melt was introduced into a molecular distiller, bis (2-hydroxyethyl) terephthalate was evaporated under the conditions of 8.1 Pa and 188 ° C., and cooled to 120 ° C. with a condenser, whereby 7.0 g of purified bis (2 -Hydroxyethyl) terephthalate was obtained. The purity of the obtained bis (2-hydroxyethyl) terephthalate was 98.3% by weight and the optical density was 0.002.

[Comparative Example 1]
The same X-ray photographic film as in Example 1 was cut into flakes of about 1 cm square, and the photographic image layer of the flakes was not peeled off and subjected to the depolymerization step as it was. The resulting depolymerized solution was colored blue, and solid foreign matters (photographic image components and the like) that were not decomposed (depolymerized) were floating. When this depolymerized solution was passed through a basket type strainer having a pore diameter of 1 mm, solid foreign substances that were not decomposed were clogged with the strainer shortly after the start of liquid passing, and the first-stage filtration treatment became impossible.

  Since the method of the present invention can efficiently recover high purity ester monomers from photographic film, particularly used X-ray photographic film, by chemical recycling, it can be expected to contribute to the recycling industry.

Claims (8)

A method for recovering an ester monomer from a photographic film in which a photographic image layer is laminated on a polyester base film,
(1) A photographic image layer peeling step in which flakes of a photographic film are immersed in an aqueous solution of an alkali compound and heat-treated at a temperature of 50 to 100 ° C. to dissolve or peel the photographic image layer;
(2) A flake separation step for separating flakes from the mixed liquid obtained in the photographic image layer peeling step,
(3) A depolymerization step in which the polyester component of the flakes separated in the flake separation step is depolymerized with a diol in the presence of a depolymerization catalyst, and (4) a depolymerization solution containing the ester monomer obtained in the depolymerization step is purified. A monomer purification and recovery step for obtaining a purified ester monomer by being treated;
Of recovering ester monomers from a photographic film comprising The method of claim 1 wherein the polyester component of the photographic film is polyethylene terephthalate. The method of Claim 1 or 2 that the usage-amount of the aqueous solution of an alkali compound is 1-10 weight part per 1 weight part of flakes of a photographic film. The method according to any one of claims 1 to 3, wherein the alkali compound is an alkali metal compound or an alkaline earth metal compound. The method as described in any one of Claims 1-4 whose content of the alkali compound in the aqueous solution of an alkali compound is 0.5 to 10 weight%. The method according to any one of claims 1 to 5, wherein the diol used in the depolymerization step is ethylene glycol. The method according to any one of claims 1 to 6, wherein the monomer purification and recovery step comprises filtration, activated carbon, ion exchange, crystallization, low boiling point evaporation, molecular distillation, or a combination thereof. . The method as described in any one of Claims 1-7 in which a monomer refinement | purification collection process includes the process crystallized with polar organic solvents other than the diol used at a depolymerization process.